As is known, the formation of extruded foam bodies in the form of boards, planks, billets, etc., can be enhanced by the employment of a vacuum chamber wherein expansion of continuously extruded foamable material is accomplished under sub-atmospheric pressure. This, however, necessitates removal of the foamed extrudate from the vacuum chamber, and to do so without adversely affecting the controlled environment (reduced pressure) in such chamber has presented a difficult problem for solution.
One known solution to this problem involves the employment of an inclined barometric leg which permits continuous removal of the extrudate from a vacuum chamber at the top of the leg in either continuous or descrete lengths to the atmosphere without affecting the reduced pressure within the vacuum chamber. For further details of this technique, reference may be had to prior U.S. Pat. Nos. 3,704,083 and 4,044,084.
Another solution to the extraction problem is set forth in copending U.S. application Ser. No. 537,832, filed Sept. 30, 1983, and entitled "Process and Apparatus for Producing Foamed Synthetic Resin Bodies." This solution generally involves the continuous extrusion of foamable material into a reduced pressure chamber or zone, cutting the foamed extrudate to length in such reduced pressure chamber, transferring the cut length into a second contiguous chamber or zone which cylically alternates between such reduced pressure and atmospheric pressure, such transfer being effected when the second chamber is at reduced pressure, and then discharging the cut length from the second chamber to the atmosphere when such second chamber is at atmospheric pressure. Although such solution generally is advantageous, the extraction procedure requires a large number of vacuum cycles per hour in order to achieve a desired level of output. For example, an extrusion rate of 50 feet per minute would require 375 vacuum cycles per hour. Moreover, the required cycle time would be relatively short thus necessitating the usage of a relatively large vacuum pump and/or accummulater system. It also is noted that there is no provision for a relatively long residence time for the cut lengths at reduced pressure as may be desired to allow full expansion, cooling and dimensional stabilization thereof, except perhaps by operating at correspondingly slow extrusion rates or by employing a correspondingly long reduced pressure chamber.